FRIEDRICH HEINRICH JACOBI (1743-1819), German philosopher, was born at Dusseldorf on the 25th of January 1743. The second son of a wealthy sugar merchant near Dusseldorf, he was educated for a commercial career. Of a retiring, meditative disposition, Jacobi associated himself at Geneva mainly with the literary and scientific circle of which the most prominent member was Lesage. He studied closely the works of Charles Bonnet, and the political ideas of Rousseau and Voltaire. In 1763 he was called back to Dusseldorf, and in the following year he married and took over the management of his father's business. After a short period he gave up his commercial career, and in 1770 became a member of the council for the duchies of Jiilich and Berg, in which capacity he distinguished himself by his ability in financial affairs, and his zeal in social reform. Jacobi kept up his interest in literary and philosophic matters by an extensive correspondence, and his mansion at Pempelfort, near Dusseldorf, was the centre of a distinguished literary circle. With C. M. Wieland he helped to found a new literary journal. Der Teutsche Mercur, in which some of his earliest writings, mainly on practical or economic subjects, were published. Here too appeared in part the first of his philosophic works, Edward Allwills Briefsammlung (1776), a combination of romance and speculation. This was followed in 1779 by Woldemar, a philosophic novel, of very imperfect structure, but full of genial
ideas, and giving the most complete picture of Jacobi's method of philosophizing. In 1779 he visited Munich as member of the privy council, but after a short stay there differences with his colleagues and with the authorities of Bavaria drove him back to Pempelfort. A few unimportant tracts on questions of theoretical politics were followed in 1785 by the work which first brought Jacobi into prominence as a philosopher. A conversation which he had held with Lessing in 178o, in which Lessing avowed that he knew no philosophy, in the true sense of that word, save Spinozism, led him to a protracted study of Spinoza's works. The Briefe uber die Lehre Spinozas (1785; 2nd ed., much enlarged and with important Appendices, 1789) expressed sharply and clearly Jacobi's strenuous objection to a dogmatic system in philosophy, and drew upon him the vigorous enmity of the Berlin clique, led by Moses Mendelssohn. Jacobi was ridiculed as endeavouring to reintroduce into philosophy the antiquated notion of unreasoning belief, was denounced as an enemy of reason, as a pietist, and as in all probability a Jesuit in disguise, and was especially attacked for his use of the ambiguous term " belief." Jacobi's next important work, David Hume uber den Glauben, oder Idealismus and Realismus (1787), was an attempt to show not only that the term Glaube had been used by the most eminent writers to denote what he had employed it for in the Letters on Spinoza, but that the nature of the cognition of facts as opposed to the construction of inferences could not be otherwise expressed. In this writing, and especially in the Appendix, Jacobi came into contact with the critical philosophy, and subjected the Kantian view of knowledge to searching examination.
The outbreak of the war with the French republic induced Jacobi in 1793 to leave his home near Dusseldorf, and for nearly ten years he resided in Holstein. While there he became intimately acquainted with Reinhold (in whose Beitrage, pt. iii., 1801, his important work Uber das Unternehmen des Kriticismus, die Vernunft zu Verstande zu bringen was first published), and with Matthias Claudius, the editor of the Wandsbecker Bote. During the same period the excitement caused by the accusation of atheism brought against Fichte at Jena led to the publication of Jacobi's Letter to Fichte (1799), in which he made more precise the relation of his own philosophic principles to theology. Soon after his return to Germany, Jacobi received a call to Munich in connexion with the new academy of sciences just founded there. The loss of a considerable portion of his fortune induced him to accept this offer; he settled in Munich in 1804, and in 1807 became president of the academy. In 1811 appeared his last philosophic work, directed against Schelling specially (Von den gottlichen Dingen and ihrer Offenbarung), the first part of which, a review of the Wandsbecker Bote, had been written in 1798. A bitter reply from Schelling was left without answer by Jacobi, but gave rise to an animated controversy in which Fries and Baader took prominent part. In 1812 Jacobi retired from the office of president, and began to prepare a collected edition of his works. He died before this was completed, on the loth of March 181g. The edition of his writings was continued by his friend F. Koppen, and was completed in 1825. The works fill six volumes, of which the fourth is in three parts. To the second is prefixed an introduction by Jacobi, which is at the same time an introduction to his philosophy. The fourth volume has also an important preface.
The philosophy of Jacobi is essentially unsystematic. A certain fundamental view which underlies all his thinking is brought to bear in succession upon those systematic doctrines which appear to stand most sharply in contradiction to it, and any positive philosophic results are given only occasionally. The leading idea of the whole is that of the complete separation between understanding and apprehension of real fact. For Jacobi understanding, or the logical faculty, is purely formal or elaborative, and its results never transcend the given material supplied to it. From the basis of immediate experience or perception thought proceeds by comparison and abstraction, establishing connexions among facts, but remaining in its nature mediate and finite. The principle of reason and consequent, the necessity of thinking each given fact of perception as conditioned, impels understanding towards an endless series of identical propositions, the records of successive comparisons and abstractions. The
province of the understanding is therefore strictly the region of the conditioned; to it the world must present itself as a mechanism. If, then, there is objective truth at all, the existence of real facts must be made known to us otherwise than through the logical faculty of thought; and, as the regress from conclusion to premises must depend upon something not itself capable of logical grounding, mediate thought implies the consciousness of immediate truth. Philosophy therefore must resign the hopeless ideal of a systematic (i.e. intelligible) explanation of things, and must content itself with the examination of the facts of consciousness. It is a mere prejudice of philosophic thinkers, a prejudice which has descended from Aristotle, that mediate or demonstrated cognition is superior in cogency and value to the immediate perception of truths or facts.
As Jacobi starts with the doctrine that thought is partial and limited, applicable only to connect facts, but incapable of explaining their existence, it is evident that for him any demonstrative system of metaphysic which should attempt to subject all existence to the principle of logical ground must be repulsive. Now in modern philosophy the first and greatest demonstrative system of 'meta-physic is that of Spinoza, and it lay in the nature of things that upon Spinoza's system Jacobi should first direct his criticism. A summary of the results of his examination is thus presented (Werke, i. 216–223): (I) Spinozism is atheism; (2) the Kabbalistic philosophy, in so far as it is philosophy, is nothing but undeveloped or confused Spinozism: (3) the philosophy of Leibnitz and Wolff is not less fatalistic than that of Spinoza, and carries a resolute thinker to the very principles of Spinoza; (4) every demonstrative method ends in fatalism; (5) we can demonstrate only similarities (agreements, truths conditionally necessary), proceeding always in identical propositions; every proof presupposes something already proved, the principle of which is immediately given (Offenbarung, revelation, is the term here employed by Jacobi, as by many later writers, e.g. Lotze, to denote the peculiar character of an immediate, unproved truth) ; (6) the keystone (Element) of all human knowledge and activity is belief (Glaube). Of these propositions only the first and fourth require further notice. Jacobi, accepting the law of reason and consequent as the fundamental rule of demonstrative reasoning, and as the rule explicitly followed by Spinoza, points out that, if we proceed by applying this principle so as to recede from particular and qualified facts to the more general and abstract conditions, we land ourselves, not in the notion of an active, intelligent creator of the system of things, but in the notion of an all-comprehensive, indeterminate Nature, devoid of will or intelligence. Our unconditioned is either a pure abstraction, or else the impossible notion of a completed system of conditions. In either case the result is atheism, and this result is necessary if the demonstrative method, the method of understanding, is regarded as the only possible means of knowledge. Moreover, the same method inevitably lands in fatalism. For, if the action of the human will is to be made intelligible to understanding, it must be thought as a conditioned phenomenon, having its sufficient ground in preceding circumstances, and, in ultimate abstraction, as the outflow from nature which is the sum of conditions. But this is the fatalist conception, and any philosophy which accepts the law of reason and consequent as the essence of understanding is fatalistic. Thus for the scientific understanding there can be no God and no liberty. It is impossible that there should be a God, for if so he would of necessity be finite. But a finite God, a God that is known, is no God. It is impossible that there should be liberty, for if so the mechanical order of phenomena, by means of which they are comprehensible, would be disturbed, and we should have an unintelligible world, coupled with the requirement that it shall be understood. Cognition, then, in the strict sense, occupies the middle place between sense perception, which is belief in matters of sense, and reason, which is belief in supersensuous fact.
The best introduction to Jacobi's philosophy is the preface to the second volume of the Works, and Appendix 7 to the Letters on Spinoza's Theory. See also J. Kuhn, Jacobi and die Philosophie seiner Zeit (1834); F. Deycks, F. H. Jacobi im Verhdltnis zu seinen Zeitgenossen (1848) ; H. Diintzer, Freundesbilder aus Goethes Leben (1853); E. Zirngiebl, F. II. Jacobis Leben, Dichten, and Denken, 1867; F. Harms, Ober die Lehre von F- H. Jacobi ,(1876). Jacobi's Auserlesener Briefwechsel has been edited by F. Roth in 2 vols. (1825–1827).